Railway tank cars are commonly used to transport liquid commodities that must be heated to enable the material to flow and unload through the bottom or top mounted discharge valve. At the present time, the material is heated by steam which passes through coils positioned on the exterior surface of the car or by coils which are positioned in the interior of the car. Typical of the prior art devices may be found in U.S. Pat. Nos. 2,145,614; 2,558,648; 2,772,784; 3,143,108; 3,176,764; 3,228,466; 3,595,307; and 3,685,458.
U.S. Pat. No. 2,145,614 discloses internal and external heating coils. U.S. Pat. No. 2,558,648 shows a heating coil secured exteriorly to a lower portion of a tank car. U.S. Pat. No. 2,772,784 describes the use of a cylindrical jacket encompassing the tank car for the purpose of applying heating from hot water flowing through the jacket. U.S. Pat. No. 3,142,108 shows a plurality of pans attached to the bottom portion of a truck trailer tank for supplying heat to the tank. U.S. Pat. No. 3,176,764 describes an integral-coil tank wall section associated with the lower portion of a tank car to transfer heat to the tank car. U.S. Pat. No. 3,228,466 shows an external heating arrangement for a storage tank. U.S. Pat. No. 3,595,307 shows another arrangement of a heating system disposed exteriorly of a tank car. Finally, U.S. Pat. No. 3,685,458 describes a heating assembly secured exteriorly to a bottom portion of a tank car.
It is apparent from the above-identified patents that there are large areas of the cars that are not subject to the heated steam and that the tank saddles and underframes attached to the bottom end of the tank act as large heat sinks which radiate heat out to the air rather than inwardly to the product. A problem also associated with the external and internal coils is that they are substantially horizontally disposed which makes them difficult to drain after the steam has been disconnected thereby causing freezing and corrosion and subsequent failure to the coils.
Still another problem associated with the prior art is that the material at the upper end of the tank is heated faster than the material at the bottom of the tank. The material at the upper portion of the tank is heated for longer than is desirable since the material will not begin to flow from the tank until the material around the discharge valve has been sufficiently heated to enable it to flow from the tank. Still another problem associated with the prior art devices is that a "boot" of material is formed in the bottom end of the car. The "boot" forms due to some commodity precipitants going to the bottom of the car due to heating and to lack of agitation. The "boot" also forms due to the heat sink effect of the steel attached to the tank at this particular location. The "boot" is the product remaining in the car after the car has been unloaded and the "boot" keeps building or accumulating thereby reducing the effective capacity of the car. At some time, the "boot" must be removed by chipping or other manual removal process.
Also, the prior art rail tank car using heated coils is not too suitable for the unloading of congealable, heat sensitive materials. Because of this, many problems have been incurred.
First, the quality of the many commodities has been affected due to over heating. On certain materials, overheating has caused the complete rejection of the commodity by the customer.
Second, heating by present methods has proven ineffective due to the problem of film buildup on the surfaces. This is caused by the settlin9 of solids to the bottom of the car during the heating process. If not removed, the baking of the product to the surface will greatly reduce heating efficiency. The boot upon heating can also cause corrosion of the bottom of the tank.
The third, and often overlooked problem, is contamination of new high quality material by burnt commodity or heel.
Fourth is the hazard which is presented to a person who must enter this enclosed environment to remove settled or burnt material.
The concept being proposed is the use of a heat system to be installed in the bottom of a tank car with sufficient slope to permit total drainage of the commodity. Such a system would concentrate the heat in the bottom of the car to obtain maximum transfer of heat at the bottom of the commodity (lading). The heated portion of the lading, as it rises through the lading causes the unheated portions of the lading to descend to the bottom to effectively cause mixing or rolling of the lading. Such thorough and uniform heating of the lading prepares the lading for faster unloading and prevents the lading being subjected to excessive heat which burns or caramelizes the lading. Also, the application of the heat at the bottom of the lading causes faster melting of the lading in and around the outlet valve
Heating efficiency is greater with the new system during unloading because the entire heating surface remains in contact with the lading during the unloading until the tank is almost empty. Coil cars lose heating efficiency through exposure of coils as the lading level drops in the car.
Initial tests indicate that the use of a heated exchanger in contact with the bottom of the lading improves heating efficiency. Data taken, using a series of probes located in tank cars, with readings taken every five minutes, proved that the improved heat system gave uniform heating of the contents. It was noted during the tests that a rolling action occurred during the heating process, and the lading turned, allowing mixing of the hot and cold portions.
In the tests, an external coil tank car and a plate (novel heat exchanger) tank car of equal capacity were used. Temperature probes were installed 6", 24", and 42" above the bottom of each tank car at the center. The boiler pressure was maintained at 76 to 80 PSI and the condensate was monitored for volume and termperature. In the coil tank car, the condensate flow was 3 gallons per minute with temperatures of the condensate reading 70.degree. F. or less for the first 1 and 1/2 hours, and then rising to a final temperature of 90.degree. F. In the plate tank car, the same procedure was followed as for the coil tank car, but the condensate temperature rose rapidly to 135.degree. F. and held at a steady pace, requiring less than half of the previous time.
The temperatures in the coil tank car rose rapidly in the top portions of the lading when compared with the temperatures at the bottom portion of the lading. This heat layering was noted and monitored after 2 hours of heating, at which time, rolling or mixing action was noted. To determine this rolling action, dye was periodically added to both cars. The plate tank car showed rapid movement of the lading due to the concentration of the heat at the bottom of the car, while the coil tank car showed very slow mixing. The lading in both of the tank cars consisted of water.
Another test was run on the plate tank car only. The test was conducted using an animal fat (congealed). The heat exchanger heated the fat rapidly, then, as the rolling action started, the temperature dropped off and paralleled the temperature rise of the lading. It was noted that the valve outlet area temperature rose rapidly. This is important, for the faster the valve temperature rises, liquifying the lading in this area, the quicker the unloading can begin.
In another test, a plate tank car was filled with blackstrap molasses, which weighs 11.5 pounds per gallon. In 5 minutes, the heat system was raised to a temperature of 80.degree. F., and the temperature around the valve outlet was at 59.degree. F. The temperature of the molasses rose evenly throughout and there were no layers of heat in the molasses, as usually happens in present coil tank cars, wherein there is a hot layer of lading at the top and a cold layer of the lading at the bottom. The plate car was then ready to be unloaded in 15 minutes after application of the heat. After the pumping was completed, there was no molasses left in the tank car, and the lading that was removed was tested. None of this lading was burned (caramelized), which is common in high sugar products in present coil tank cars.
Thus, it can be seen that the invention accomplishes at least all of the stated objectives, which are more specifically reiterated hereinbelow:
Since units of the heat exchanger are sloped, substantially all of the condensate is drained out and the heat exchanger is not subject to any freezing.
Since the lading is substantially resting on top of the heat exchanger which applies heat over a large area of the lading, no air pockets or hot spots occur as they do in an external coil prior art tank car.
A tank car using the inventive heat exchanger, as opposed to the prior art external coil tank car, unloads much faster than the coil tank car in winter.
No cooking of the lading occurs because the heat exchanger applies uniform heat over a large area of the lading.
Approximately 4/5ths to 5/6ths of the subject tank car is empty before any portion of the heat system (heat exchange units) is exposed to the atmosphere in the tank, as opposed to the prior art internal pipe coils and external coils which are completely exposed when the tank car is 7/8ths empty. Therefore, the inventive heat system continues to be in contact with the lading and heat the lading, keeping it fluid until the tank car is empty.
The pitch of each heat exchanger unit of almost 1:12 (8% grade) assures a complete unloading and prevents material buildup.
All of the heat is at the bottom of the tank car, and as the heat rises, the tank car will unload much faster, saving BTU (British Thermal Units) costs. The side coils on an external coil car do not do much good because the heat goes about 8 inches into the lading and goes through commodity to the top of the tank car. Also coils at sides of car are closer to top of car and overheat the top of the car.
By positioning the heating system off the floor of the tank car, heat sinks caused by the tank cradles, body bolsters, and trucks are non-existent or eliminated.
External coils on a coil car are positioned or spaced from one another a minimum of 6 inches between the welded positions which cause a lot of dead spots between the coils and such coils are spaced even farther apart on the bottom of the car in order to miss the stub sills and body webbing, as opposed to the inventive heat system which provides a solid (i.e. substantially continuous) heating surface at the bottom of the tank car.
In view of the flow arrangement in the heat exchanger, there is no need to steam jacket the outlet valve.
Because of the slope possessed by each unit of the heat exchanger and the rolling action of lading caused by the heating action and the slope of the heat exchanger, there is no corrosion or product buildup, as opposed to the formation of a boot in an external coil tank car, which boot cuts down on the efficiency of heat transfer on the bottom coils of the tank car and which acts as an undesirable heat insulator.
The application of heat at the bottom of the lading creates internal circulation commencing at the bottom, then upwardly through the lading, causing the cool portions of the lading to move downwardly towards the bottom, thereby creating a rolling or mixing action, resulting in a faster and uniform heating of the lading.
Since the present heating system uniformly heats the lading, the temperatures of the heating medium need not be excessive, thereby avoiding damage to plastic linings used within the tank cars, as would occur in a coil tank car.
Further, in a modified form of the invention, heat exchanger is provided with appropriate ports for the immediate purging of any condensate forming in the heat exchanger. The foregoing avoids a buildup of the condensate which opposes the introduction of the pressurized heating medium. Also such condensate buildup saps the incoming heat so that it is revaporized. In cold weather, the buildup of condensate forms a liquid plug which has to be bodily moved forward by the incoming heating medium, thereby requiring an increase in the pressure of the incoming heating medium.
Therefore, it is a principal object of the invention to provide an improved heated tank car.
A further object of the invention is to provide a heated tank car having a heat exchanger provided in the interior thereof with the heat exchanger being insulatingly spaced above the bottom of the tank to achieve a more efficient and uniform heating of the material.
A still further object of the invention is to provide a heated tank car which eliminates the heat sink problems normally associated with conventional heated tank cars.
Still another object of the invention is to provide a heat exchanger for a tank car which is sloped towards the middle of the car so that condensate will drain from the heat exchanger thereby reducing corrosion of the heat exchanger.
Still another object of the invention is to provide a heated tank car which prevents the formation of a "boot" at the bottom of the car.
A further object of the invention is to provide drainage means in the heat exchanger for purging any heating medium condensate that may form within the heat exchanger.
Still another object of the invention is to provide a heated tank car employing an inclined heat exchanger therein to assist the flow of material to the discharge valve of the car.
These and other objects will be apparent to those skilled in the art.